1. Field of the Invention
The present invention relates to a scintillation probe for the measurement of beta dose rates. In particular, the invention minimizes the effects of higher energy particles, x-rays and gamma rays upon the measurement.
2. Description of the Prior Art
The beta dose to skin tissue is defined by the National Council on Radiation Protection as the dose to the thin layer of basal epithelial tissue lying at an average depth of 7 mg/cm.sup.2 or, alternatively, by the International Commission on Radiological Protection as the dose to the skin tissue lying between 5 mg/cm.sup.2 and 10 mg/cm.sup.2.
It is known to use thin scintillators covered by an aluminized Dupont MYLAR window to provide a skin-equivalent structure for detecting beta particles. The scintillator is coupled to a photomultiplier by a tissue equivalent light pipe. Such a device is described in Martz et al, Field Tests of a Portable Tissue Equivalent Survey Meter for Monitoring Mixed Beta/Gamma Radiation Fields, Office of Nuclear Regulatory Research, Division of Radiation Programs and Earth Sciences, U.S. Nuclear Regulatory Commission, NUREG/CR-4553, EGG-2448, May 1986, and is incorporated herein by reference in its entirety.
Unfortunately, the output of the photomultiplier in this known device includes not only the skin equivalent beta dose rate, but also Cerenkov light from higher energy particles and electrons produced directly in the photomultiplier cathode by x-rays and gamma rays.
Because the Cerenkov light and the gamma ray and x-ray components exhibit characteristically narrow pulse shapes, sophisticated high speed electronics can be used to electronically remove their contribution. These electronics substantially increase the complexity and cost of the device.